The use of solid fuel such as wood or coal in place of oil is increasingly popular in view of the high cost and possible scarcity of oil, and substantial research has been conducted to provide heaters or furnaces of the closed controlled-combustion type to provide for maximum efficiency in heat extraction and minimizing heat loss through the chimney. For use as a source of heat for extended periods of time without the nuisance of repeated loadings these known heaters or furnaces are of the closed controlled-combustion type wherein the degree of combustion is governed by controlling the air entering the heater. Such heaters and furnaces are predominantly used at a level less than 50% of maximum burn and it is known that at such lower temperatures much of the fuel in the form of combustible gases and pollutants flow up the chimney where deposits of creosote present the danger of fire and the ejection of these unburned gases and pollutants is damaging to the environment.
Increasingly stringent clean air laws are presently being proposed to limit the pollutant discharge from domestic solid fuel burning heaters and furnaces and the purpose of the present invention is not only to provide a high efficiency heater for the burning of wood or coal, but also to reduce the pollutants and combustible gases expelled from the heater.
To applicant's knowledge, the clean burn heaters presently on the market and which do not include expensive catalyst combustors to further combust and clean the smoke prior to discharge are effective in pollution control only if operated at about 50% and above the maximum burn, and are ineffective in this regard at lower burn rates.